THURSDAY, May 3, 2018 (HealthDay News) -- It's been long known that people who sit for extended periods of time run the risk of blood clots.

In fact, the condition has been dubbed economy class syndrome because it's believed it can be brought on by stretches of prolonged immobility on long-distance flights.

Now, a new study out of Japan found that people fleeing a natural disaster seemed to be at risk of the unexpected cause of death -- life-threatening blood clots in the legs and lungs triggered by sitting in a car for a long time.

The findings highlight the importance of educating people about the clot risk, experts say.

In the study, researchers explained that following the 2016 Kumamoto earthquake in Japan, a large number of night aftershocks occurred. Many people were afraid to return home and decided to evacuate instead. While some reached a public evacuation shelter, many others had to stay in their vehicles overnight.

An analysis of hospital data following this event revealed an "epidemic" of blood clots in evacuees' legs. In some cases, these blood clots traveled to the lungs.

Specifically, 51 evacuees were hospitalized for blood clots in the legs. Of those, 42 (82 percent) had spent the night in a vehicle. In 35 patients, blood clots in the legs traveled to the lungs, a life-threatening condition called pulmonary embolism.

The study findings were published May 3 in the Canadian Journal of Cardiology.

The findings show the need to educate people about the risk and prevention of venous thromboembolism (VTE), the study authors said in a journal news release.

"Preventive awareness activities by professional medical teams, supported by education in the media about the risk of VTEs after spending the night in a vehicle, and raising awareness of evacuation centers, could lead to a reduced number of victims of VTE," said lead investigator Dr. Seiji Hokimoto. He's with the department of cardiovascular medicine at Kumamoto University, in Japan.

According to Dr. Stanley Nattel, journal editor-in-chief, "This is a dramatic example of the risks inherent in spending prolonged periods immobilized in a cramped position."

Nattel added that the report "is an important reminder of a public health point, and reinforces the need to get up and walk around regularly when on an airplane or when forced to stay in a car for a long time."